Thickness determination of black phosphorususing Raman spectroscopy

Abstract

Black phosphorus is a 2-D layered material. Since the isolation of a single
layer of black phosphorus in 2014, it has garnered a great deal of interest due
to several rare properties such as anisotropy, high conductivity, and tunable
bandgap. These properties make it an ideal candidate for a wide variety of applications and provide a means for analyzing particular direction-dependent
physical phenomena. However, due to its unique structure, many of the 2-D
material properties are orientation and thickness dependent. Thus the study
and application of this material are dependent on effective methods for characterizing orientation and thickness. This project introduces a method to
determine the thickness of mechanically exfoliated black phosphorus flakes
utilizing Raman spectroscopy. The advantage of Raman spectroscopy to
other measurement techniques is that it is a non-destructive method capable
of quickly measuring multiple black phosphorus flakes.

Popular Abstract

We are all familiar with graphite – the material used to make your pencil
lead. You may even be aware that graphite can be pulled apart to obtain
a single layer, one atom, thick known as graphene. In 2004 graphene was
isolated for the first time. Since then, it has been much touted due to its
unique properties and the technological advancements these properties could
deliver. This is not without good reason due to a myriad of unique properties; it could revolutionize batteries, construction materials, and much more.
Despite all of its remarkable properties, graphene cannot do it all. Graphene
is a conductor; however, the basis for electronic and optoelectronic devices
are semiconductors. Semiconductors are a class of materials that are circumstantially conductive. Each semiconductor has what is known as a band
gap. If enough energy is applied to overcome the band gap, it will behave
like a conductor. The band gap can be used as a switch for electronics -
an applied voltage larger than the band gap can turn a device on or off. It
can also convert light to electricity as with solar cells or from electricity to
light as with a laser. Fortunately, in 2014, phosphorene – a single layer of
black phosphorus – was isolated. Phosphorene has many of the properties
that make graphene attractive, but it is a semiconductor. Furthermore, it
is a semiconductor with a tunable bandgap. That is, the amount of energy
required to make it conductive can be varied. This is a very exciting feature
for design purposes. One of the primary factors determining phosphorene’s
bandgap is the number of phosphorene layers stacked on top of one another.
The number of layers has other important design implications as the number
of layers also determines the heat conductivity of the black phosphorus. The
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heat conductivity must be known to understand how to design components
that do not overheat during operation. This brings us to the purpose of
this study - to determine the thickness of black phosphorus samples. The
thickness cannot be determined by regular means as there is no ruler small
enough; rather than measurements on the scale of centimeters or even millimeters, the scale involved here is nanometers - one billionth of a meter. In
this case, we will measure the thickness with a laser. A black phosphorus
sample will be placed on a silicon wafer; the reflected light will be observed
using an array of charged coupled devices - the same basic building blocks
of a digital camera. The sample will be moved so that the laser is for one
measurement incident on just the silicon substrate and for another will pass
through the black phosphorus. Because the sample will block some of the
reflected light, dependent on its thickness, the amount of light blocked can be
used to determine the thickness. This is an essential step in commercializing
black phosphorus, which promises many new exciting advances in electronics,
communication, energy, and much more.

• author: Kasper, Blake
• supervisor: Jörgen Larsson; Eric Nilsson
• organization: Atomic Physics; Department of Physics
• course: FYSM30 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: Raman Spectroscopy, Black Phosphorus, Phosphorene
• language: English
• id: 9067749
• date added to LUP: 2022-01-28 09:28:54
• date last changed: 2022-01-28 09:28:54